Ccn pv7 route_lab2-1_eigrp-load-balancing_student

CCNPv7 ROUTE
Chapter 2 Lab 2-1, EIGRP Load Balancing
Topology
Objectives
• Review a basic EIGRP configuration.
• Explore the EIGRP topology table.
• Identify successors, feasible successors, and feasible distances.
• Use show and debug commands for the EIGRP topology table.
• Configure and verify equal-cost load balancing with EIGRP.
• Configure and verify unequal-cost load balancing with EIGRP.
Background
As a senior network engineer, you are considering deploying EIGRP in your corporation and want to evaluate its
ability to converge quickly in a changing environment. You are also interested in equal-cost and unequal-cost load
balancing because your network contains redundant links. These links are not often used by other link-state routing
protocols because of high metrics. Because you are interested in testing the EIGRP claims that you have read about,
you decide to implement and test on a set of three lab routers before deploying EIGRP throughout your corporate
network.
© 2014 Cisco and/or its affiliates. All rights reserved. This document is Cisco Public. Page 1 of 21

CCNPv7 ROUTE Lab 2-1, EIGRP Load Balancing
Note: This lab uses Cisco 1941 routers with Cisco IOS Release 15.4 with IP Base. Depending on the Cisco IOS
Software version, the commands available and output produced might vary from what is shown in this lab.
Required Resources
• 3 routers (Cisco IOS Release 15.2 or comparable)
• Serial and Ethernet cables
Step 0: Suggested starting configurations.
a. Apply the following configuration to each router along with the appropriate hostname. The exec-timeout 0 0
command should only be used in a lab environment.
Router(config)# no ip domain-lookup
Router(config)# line con 0
Router(config-line)# logging synchronous
Router(config-line)# exec-timeout 0 0
Step 1: Configure the addressing and serial links.
b. Create three loopback interfaces on each router and address them as 10.1.X.1/30, 10.1.X.5/30, and 10.1.X.9/30,
where X is the number of the router. Use the following table or the initial configurations located at the end of the
lab.
Router Interface IP Address/Mask
R1 Loopback11 10.1.1.1/30
R1 Loopback15 10.1.1.5/30
R1 Loopback19 10.1.1.9/30
R2 Loopback21 10.1.2.1/30
R2 Loopback25 10.1.2.5/30
R2 Loopback29 10.1.2.9/30
R3 Loopback31 10.1.3.1/30
R3 Loopback35 10.1.3.5/30
R3 Loopback39 10.1.3.9/30
R1(config)# interface Loopback 11
R1(config-if)# ip address 10.1.1.1 255.255.255.252
R1(config-if)# exit
R1(config-if)# exit
R1(config-if)# exit
R2(config-if)# exit
R2(config-if)# exit

R2(config-if)# exit
R3(config-if)# exit
R3(config-if)# exit
R3(config-if)# exit
c. Specify the addresses of the serial interfaces as shown in the topology diagram. Set the clock rate to 64 kb/s, and
manually configure the interface bandwidth to 64 kb/s.
Note: If you have WIC-2A/S serial interfaces, the maximum clock rate is 128 kb/s. If you have WIC-2T serial
interfaces, the maximum clock rate is much higher (2.048 Mb/s or higher depending on the hardware), which is
more representative of a modern network WAN link. However, this lab uses 64 kb/s and 128 kb/s settings.
R1(config)# interface Serial 0/0/0
R1(config-if)# description R1-->R2
R1(config-if)# clock rate 64000
R1(config-if)# bandwidth 64
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config-if)# exit
R2(config-if)# exit
R2(config-if)# exit
R3(config-if)# exit

R3(config-if)# exit
d. Verify connectivity by pinging across each of the local networks connected to each router.
e. Issue the show interfaces description command on each router. This command displays a brief listing of the
interfaces, their status, and a description (if a description is configured). Router R1 is shown as an example.
R1# show interfaces description
Interface Status Protocol Description
Em0/0 admin down down
Gi0/0 admin down down
Gi0/1 admin down down
Se0/0/0 up up R1-->R2
Se0/0/1 up up R1-->R3
Lo11 up up
Lo15 up up
Lo19 up up
R1#
f. Issue the show protocols command on each router. This command displays a brief listing of the interfaces, their
status, and the IP address and subnet mask configured (in prefix format /xx) for each interface. Router R1 is
shown as an example.
R1# show protocols
Global values:
Internet Protocol routing is enabled
Embedded-Service-Engine0/0 is administratively down, line protocol is down
GigabitEthernet0/0 is administratively down, line protocol is down
GigabitEthernet0/1 is administratively down, line protocol is down
Serial0/0/0 is up, line protocol is up
Internet address is 10.1.102.1/29
Serial0/0/1 is up, line protocol is up
Loopback11 is up, line protocol is up
R1#
Step 2: Configure EIGRP.
a. Enable EIGRP AS 100 for all interfaces on R1 and R2 using the commands. Do not enable EIGRP yet on R3. For
your reference, these are the commands which can be used:
R1(config)# router eigrp 100
R1(config-router)# network 10.0.0.0
b. Use the debug ip routing and the debug ip eigrp 100 commands to watch EIGRP install the routes in the
routing table when your routers become adjacent. (Note: The type of output you receive may vary depending
upon the IOS.) You get output similar to the following.
R3# debug ip routing

IP routing debugging is on
R3# debug ip eigrp 100
R3# conf t
Enter configuration commands, one per line. End with CNTL/Z.
*Jun 22 11:06:09.315: RT: add router 2048, all protocols have local database
*Jun 22 11:06:18.591: %DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor 10.1.103.1
(Serial0/0/0) is up: new adjacency
(Serial0/0/1) is up: new adjacency
*Jun 22 11:06:19.055: RT: updating eigrp 10.1.102.0/29 (0x0) :
via 10.1.103.1 Se0/0/0 0 1048578
*Jun 22 11:06:19.055: RT: add 10.1.102.0/29 via 10.1.103.1, eigrp metric
[90/41024000]
via 10.1.103.1 Se0/0/0
R3(config-router)#end 0 1048578
*Jun 22 11:06:19.055: RT: add 10.1.1.0/30 via 10.1.103.1, eigrp metric [90/40640000]
via 10.1.103.1 Se0/0/0 0 1048578
via 10.1.103.1 Se0/0/0 0 1048578
via 10.1.103.1 Se0/0/0 0 1048578
via 10.1.103.1 Se0/0/0 0 1048578
<output omitted>
R3#
R3(config-router)# end
R3#
R3#undebug all
All possible debugging has been turned off
R3#
Essentially, the EIGRP DUAL state machine has just computed the topology table for these routes and installed
them in the routing table.
c. Check to see that these routes exist in the routing table with the show ip route command.
R3# show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP

a - application route
+ - replicated route, % - next hop override
Gateway of last resort is not set
10.0.0.0/8 is variably subnetted, 17 subnets, 3 masks
D 10.1.1.0/30 [90/40640000] via 10.1.103.1, 00:10:54, Serial0/0/0
D 10.1.1.4/30 [90/40640000] via 10.1.103.1, 00:10:54, Serial0/0/0
D 10.1.1.8/30 [90/40640000] via 10.1.103.1, 00:10:54, Serial0/0/0
D 10.1.2.0/30 [90/40640000] via 10.1.203.2, 00:10:54, Serial0/0/1
D 10.1.2.4/30 [90/40640000] via 10.1.203.2, 00:10:54, Serial0/0/1
D 10.1.2.8/30 [90/40640000] via 10.1.203.2, 00:10:54, Serial0/0/1
C 10.1.3.0/30 is directly connected, Loopback31
L 10.1.3.1/32 is directly connected, Loopback31
D 10.1.102.0/29 [90/41024000] via 10.1.203.2, 00:10:54, Serial0/0/1
[90/41024000] via 10.1.103.1, 00:10:54, Serial0/0/0
C 10.1.103.0/29 is directly connected, Serial0/0/0
L 10.1.103.3/32 is directly connected, Serial0/0/0
C 10.1.203.0/29 is directly connected, Serial0/0/1
L 10.1.203.3/32 is directly connected, Serial0/0/1
R3#
d. After you have full adjacency between the routers, ping all the remote loopbacks to ensure full connectivity.
You should receive ICMP echo replies for each address pinged.
e. Verify the EIGRP neighbor relationships with the show ip eigrp neighbors command.
R1# show ip eigrp neighbors
EIGRP-IPv4 Neighbors for AS(100)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
1 10.1.103.3 Se0/0/1 13 00:14:20 49 2340 0 6
0 10.1.102.2 Se0/0/0 10 00:29:14 37 2340 0 36
R1#
(sec) (ms) Cnt Num
1 10.1.203.3 Se0/0/1 13 00:14:28 71 2340 0 7
0 10.1.102.1 Se0/0/0 13 00:29:21 35 2340 0 36
R2#
(sec) (ms) Cnt Num
1 10.1.203.2 Se0/0/1 13 00:14:07 1305 5000 0 37
0 10.1.103.1 Se0/0/0 14 00:14:07 42 2340 0 37
R3#

Step 3: Examine the EIGRP topology table.
a. EIGRP builds a topology table containing all successor routes. The course content covered the vocabulary for
EIGRP routes in the topology table. What is the feasible distance of route 10.1.1.0/30 in the R3 topology table in
the following output?
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R3# show ip eigrp topology
EIGRP-IPv4 Topology Table for AS(100)/ID(10.1.3.9)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 10.1.102.0/29, 2 successors, FD is 41024000
via 10.1.103.1 (41024000/40512000), Serial0/0/0
via 10.1.203.2 (41024000/40512000), Serial0/0/1
via 10.1.103.1 (40640000/128256), Serial0/0/0
via Connected, Loopback31
via 10.1.203.2 (40640000/128256), Serial0/0/1
via 10.1.203.2 (40640000/128256), Serial0/0/1
via Connected, Serial0/0/0
via 10.1.103.1 (40640000/128256), Serial0/0/0
via 10.1.203.2 (40640000/128256), Serial0/0/1
via 10.1.103.1 (40640000/128256), Serial0/0/0
R3#
b. The most important thing is the two successor routes in the passive state on R3. R1 and R2 are both advertising
their connected subnet of 10.1.102.0/30. Because both routes have the same feasible distance of 41024000, both
are installed in the topology table. This distance of 41024000 reflects the composite metric of more granular
properties about the path to the destination network. Can you view the metrics before the composite metric is
computed?
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c. Use the show ip eigrp topology 10.1.102.0/29 command to view the information that EIGRP has received about
the route from R1 and R2.

R3# show ip eigrp topology 10.1.102.0/29
EIGRP-IPv4 Topology Entry for AS(100)/ID(10.1.3.9) for 10.1.102.0/29
State is Passive, Query origin flag is 1, 2 Successor(s), FD is 41024000
Descriptor Blocks:
10.1.103.1 (Serial0/0/0), from 10.1.103.1, Send flag is 0x0
Composite metric is (41024000/40512000), route is Internal
Vector metric:
Minimum bandwidth is 64 Kbit
Total delay is 40000 microseconds
Reliability is 255/255
Load is 1/255
Minimum MTU is 1500
Hop count is 1
Originating router is 10.1.1.9
Vector metric:
Load is 1/255
Minimum MTU is 1500
Hop count is 1
R3#
The output of this command shows the following information regarding EIGRP:
• The bandwidth metric represents the minimum bandwidth among all links comprising the path to the
destination network.
• The delay metric represents the total delay over the path.
• The minimum MTU represents the smallest MTU along the path.
• If you do not have full knowledge of your network, you can use the hop count information to check how many
Layer 3 devices are between the router and the destination network.
Step 4: Observe equal-cost load balancing.
EIGRP produces equal-cost load balancing to the destination network 10.1.102.0/29 from R1. Two equal-cost paths
are available to this destination per the topology table output above.
a. Use the traceroute 10.1.102.1 command to view the hops from R3 to this R1 IP address. Notice that both R1 and
R2 are listed as hops because there are two equal-cost paths and packets can reach this network via either link.
R3# traceroute 10.1.102.1
Type escape sequence to abort.
Tracing the route to 10.1.102.1
VRF info: (vrf in name/id, vrf out name/id)
1 10.1.203.2 24 msec
10.1.103.1 12 msec
10.1.203.2 24 msec
R3#
Cisco IOS enables Cisco Express Forwarding (CEF), which, by default, performs per-destination load balancing.
CEF allows for very rapid switching without the need for route processing. However, if you were to ping the
destination network, you would not see load balancing occurring on a packet level because CEF treats the entire
series of pings as one flow.
CEF on R3 overrides the per-packet balancing behavior of process switching with per-destination load balancing.

b. To see the full effect of EIGRP equal-cost load balancing, temporarily disable CEF and route caching so that all IP
packets are processed individually and not fast-switched by CEF.
R3(config)# no ip cef
R3(config)# interface S0/0/0
R3(config-if)# no ip route-cache
R3(config-if)# interface S0/0/1
R3(config-if)# no ip route-cache
Note: Typically, you would not disable CEF in a production network. It is done here only to illustrate load
balancing. Another way to demonstrate per-packet load balancing, that does not disable CEF, is to use the per-
packet load balancing command ip load-share per-packet on outgoing interfaces S0/0/0 and S0/0/1.
c. Verify load balancing with the debug ip packet command, and then ping 10.1.102.1. Like any debug command,
debug ip packet should be used with caution on a production network. Without any ACL filtering, this command
will overwhelm the router’s CPU processes in a production environment. Issue the undebug all command to stop
debug processing. You see output similar to the following:
R3# debug ip packet
IP packet debugging is on
R3# ping 10.1.102.1
Sending 5, 100-byte ICMP Echos to 10.1.102.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 28/36/44 ms
R3#
R3#
*Jun 22 11:39:37.043: IP: tableid=0, s=10.1.203.3 (local), d=10.1.102.1
(Serial0/0/1), routed via RIB
*Jun 22 11:39:37.043: IP: s=10.1.203.3 (local), d=10.1.102.1 (Serial0/0/1), len
100, sending
100, sending full packet
*Jun 22 11:39:37.087: IP: s=10.1.102.1 (Serial0/0/0), d=10.1.203.3, len 100, input
feature, MCI Check(104), rtype 0, forus FALSE, sendself FALSE, mtu 0, fwdchk FALSE
*Jun 22 11:39:37.087: IP: tableid=0, s=
R3#10.1.102.1 (Serial0/0/0), d=10.1.203.3 (Serial0/0/1), routed via RIB
*Jun 22 11:39:37.087: IP: s=10.1.102.1 (Serial0/0/0), d=10.1.203.3, len 100, rcvd 4
*Jun 22 11:39:37.087: IP: s=10.1.102.1 (Serial0/0/0), d=10.1.203.3, len 100, stop
process pak for forus packet
100, sending
*Jun 22 11:39:37.087: IP: s=10.1.103.3 (local),
R3# d=10.1.102.1 (Serial0/0/0), len 100, sending full packet
*Jun 22 11:39:37.115: IP: s=10.1.102.1 (Serial0/0/0), d=10.1.103.3, len 100, input
feature, MCI Check(104), rtype 0, forus FALSE, sendself FALSE, mtu 0, fwdchk FALSE
<output omitted>
R3# undebug all
Notice that EIGRP load-balances between Serial0/0/0 (s=10.1.103.3) and Serial0/0/1 (s=10.1.203.3). This
behavior is part of EIGRP. It can help utilize underused links in a network, especially during periods of congestion.

Step 5: Analyze alternate EIGRP paths not in the topology table.
a. Issue the show ip eigrp topology command on R3 to see successors and feasible successors for each route
that R3 has learned through EIGRP..
via 10.1.103.1 (41024000/40512000), Serial0/0/0
via 10.1.203.2 (41024000/40512000), Serial0/0/1
via 10.1.103.1 (40640000/128256), Serial0/0/0
via 10.1.203.2 (40640000/128256), Serial0/0/1
via 10.1.203.2 (40640000/128256), Serial0/0/1
via 10.1.103.1 (40640000/128256), Serial0/0/0
via 10.1.203.2 (40640000/128256), Serial0/0/1
via 10.1.103.1 (40640000/128256), Serial0/0/0
R3#
Perhaps you expected to see two entries to the R1 and R2 loopback networks in the R3 topology table. Why is
there only one entry shown in the topology table?
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b. Issue the show ip eigrp topology all-links command to see all routes that R3 has learned through EIGRP. This
command shows all entries that EIGRP holds on this router for networks in the topology, including the exit serial
interface and IP address of the next hop to each destination network, and the serial number (serno) that uniquely
identifies a destination network in EIGRP.
R3# show ip eigrp topology all-links

P 10.1.102.0/29, 2 successors, FD is 41024000, serno 13
via 10.1.103.1 (41024000/40512000), Serial0/0/0
via 10.1.203.2 (41024000/40512000), Serial0/0/1
via 10.1.103.1 (40640000/128256), Serial0/0/0
via 10.1.203.2 (41152000/40640000), Serial0/0/1
via 10.1.203.2 (40640000/128256), Serial0/0/1
via 10.1.103.1 (41152000/40640000), Serial0/0/0
via 10.1.203.2 (40640000/128256), Serial0/0/1
via 10.1.103.1 (41152000/40640000), Serial0/0/0
via 10.1.103.1 (40640000/128256), Serial0/0/0
via 10.1.203.2 (41152000/40640000), Serial0/0/1
via 10.1.203.2 (40640000/128256), Serial0/0/1
via 10.1.103.1 (41152000/40640000), Serial0/0/0
via 10.1.103.1 (40640000/128256), Serial0/0/0
via 10.1.203.2 (41152000/40640000), Serial0/0/1
R3#
What is the reported distance to the R1’s loopback networks using R1 and R2 as next-hop routers?
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c. Use the show ip eigrp topology 10.1.2.0/30 command to see the granular view of the alternate paths to
10.1.2.0, including ones with a higher reported distance than the feasible distance.
IP-EIGRP (AS 100): Topology entry for 10.1.2.0/30
Routing Descriptor Blocks:
Composite metric is (40640000/128256), Route is Internal
Vector metric:

Load is 1/255
Minimum MTU is 1500
Hop count is 1
Vector metric:
Load is 1/255
Minimum MTU is 1500
Hop count is 2
When using the show ip eigrp topology command, why is the route to 10.1.2.0/30 through R1 (via 10.1.103.1)
not listed in the topology table?
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What is its reported distance from R1?
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What is its feasible distance?
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If the R2 Serial0/0/1 interface were shut down, would EIGRP route through R1 to get to 10.1.2.0/30? Why isn’t the
switch to a new path a quick as it could be?
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Record your answer, and then experiment by shutting down the R1 S0/0/1 interface while an extended ping is
running as described below.
d. Start a ping with a high repeat count on R3 to the R1 Serial0/0/0 interface 10.1.102.1.
R3# ping 10.1.102.1 repeat 10000
e. Enter interface configuration mode on R1 and shut down port Serial0/0/1, which is the direct link from R1 to R3.
R1(config)# interface serial 0/0/1
R1(config-if)# shutdown

f. When the adjacency between R1 and R3 goes down, some pings will be lost. After pings are again being
successfully received, stop the ping using Ctrl+Shift+^.
R3#ping 10.1.102.1 repeat 10000
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
<output omitted>
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!.!!!!!!
*Jun 22 12:56:45.739: %LINK-3-UPDOWN: Interface Serial0/0/1, changed state to
down!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!
(Serial0/0/1) is down: interface down
*Jun 22 12:56:46.739: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/1,
changed state to down!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
<output omitted>
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!
*Jun 22 12:57:08.723: %LINK-3-UPDOWN: Interface Serial0/0/1, changed state to up
*Jun 22 12:57:09.723: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/0/1,
changed state to
up!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!
(Serial0/0/1) is up: new
adjacency!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
R3#
How many packets were dropped?
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Note: When examining the EIGRP reconvergence speed after deactivating the serial link between R1 and R3, the
focus should not be on the count of lost ping packets but rather on the duration of connectivity loss or how long it took
to perform a successful cutover. The router waits for up to two seconds for each sent ICMP ECHO request to receive
a reply and only then does it send another ECHO request. If the router did not wait for the reply, the count of lost
packets would be much higher. Because two packets were lost, the cutover took approximately 4 seconds.
Another factor to consider is that an interface deliberately delays the information about loss of connectivity for 2
seconds to prevent transient link flaps (link going up and down) from introducing instability into the network. If the real
speed of EIGRP is to be observed, this delay can be made as short as possible using the command carrier-delay
msec 0 on all serial interfaces.
g. Issue the no shutdown command on the R1 Serial0/0/1 interface before continuing to the next step.
Step 6: Observe unequal-cost load balancing.
Topology showing modified bandwidths as configured in step 6-b.

a. Review the composite metrics advertised by EIGRP using the show ip eigrp topology 10.1.2.0/30 command,.
IP-EIGRP (AS 100): Topology entry for 10.1.2.0/30
Vector metric:
Load is 1/255
Minimum MTU is 1500
Hop count is 1
Vector metric:
Load is 1/255
Minimum MTU is 1500
Hop count is 2
The reported distance for a loopback network is higher than the feasible distance, so DUAL does not consider it a
feasible successor route.
b. To demonstrate unequal-cost load balancing in your internetwork, upgrade the path to the destination network
through R1 with a higher bandwidth. Change the clock rate and bandwidth on the R1, R2, and R3 serial interfaces
to 128 kb/s.

R1(config-if)# interface serial 0/0/1
c. Issue the show ip eigrp topology 10.1.2.0/30 command again on R3 to see what has changed.
EIGRP-IPv4 Topology Entry for AS(100)/ID(10.1.3.9) for 10.1.2.0/30
Descriptor Blocks:
Vector metric:
Load is 1/255
Minimum MTU is 1500
Hop count is 2
Vector metric:
Load is 3/255
Minimum MTU is 1500
Hop count is 1
R3#
After manipulating the bandwidth parameter, the preferred path for R3 to the loopback interfaces of R2 is now
through R1. Even though the hop count is two and the delay through R1 is nearly twice that of the R2 path, the
higher bandwidth and lower FD results in this being the preferred route.
Note: Hop count is only mentioned to help you visualize the two paths. Hop count is not part of the composite
EIGRP metric.
d. Issue the show ip route command to verify that the preferred route to network 10.1.2.0 is through R1 via
Serial0/0/0 to next hop 10.1.103.1. There is only one route to this network due to the difference in bandwidth.
R3# show ip route eigrp
<output omitted>
D 10.1.1.0/30 [90/20640000] via 10.1.103.1, 00:05:09, Serial0/0/0
D 10.1.1.4/30 [90/20640000] via 10.1.103.1, 00:05:09, Serial0/0/0
D 10.1.1.8/30 [90/20640000] via 10.1.103.1, 00:05:09, Serial0/0/0

D 10.1.2.0/30 [90/21152000] via 10.1.103.1, 00:05:09, Serial0/0/0
D 10.1.2.4/30 [90/21152000] via 10.1.103.1, 00:05:09, Serial0/0/0
D 10.1.2.8/30 [90/21152000] via 10.1.103.1, 00:05:09, Serial0/0/0
D 10.1.102.0/29 [90/21024000] via 10.1.103.1, 00:05:09, Serial0/0/0
R3#
e. The variance command is used to enable unequal-cost load balancing. Setting the variance command allows
you to install multiple loop-free paths with unequal costs into the routing table. EIGRP will always install the
successor with the best path. Additional feasible successors are candidates as for unequal-cost paths to be
included in the routing table. These candidates must meet two conditions:
• The route must be loop-free, a current feasible successor in the topology table.
• The metric of the route must be lower than the metric of the best route (successor), multiplied by the
variance configured on the router.
In the previous output, R3 shows the best path for 10.1.2.0/30 through R1 via 10.1.103.1. Examining the topology
table on R3, there is also a feasible successor to this network through R2 via 10.1.203.1.
via 10.1.103.1 (21024000/20512000), Serial0/0/0
via 10.1.203.2 (41024000/20512000), Serial0/0/1
via 10.1.103.1 (20640000/128256), Serial0/0/0
via 10.1.103.1 (21152000/20640000), Serial0/0/0
via 10.1.203.2 (40640000/128256), Serial0/0/1
via 10.1.103.1 (21152000/20640000), Serial0/0/0
via 10.1.203.2 (40640000/128256), Serial0/0/1
via 10.1.103.1 (20640000/128256), Serial0/0/0
via 10.1.103.1 (21152000/20640000), Serial0/0/0
via 10.1.203.2 (40640000/128256), Serial0/0/1
via 10.1.103.1 (20640000/128256), Serial0/0/0
R3#
f. Issue the debug ip eigrp 100 command on R3 to show route events changing in real time. Then, under the
EIGRP router configuration on R3, issue the variance 2 command, which allows unequal-cost load balancing
bounded by a maximum distance of (2) × (FD), where FD represents the feasible distance for each route in the
routing table. Using 10.1.2.0/30 as an example, (2) x (21152000) = 42304000. The FD of the feasible successor is

40640000 which is less that the variance-modified FD of 42304000. Therefore, the feasible successor route
become an additional successor and is added to the routing table.
R3# debug ip eigrp 100
EIGRP-IPv4 Route Event debugging is on for AS(100)
R3# conf t
Enter configuration commands, one per line. End with CNTL/Z.
R3(config-router)# variance 2
R3(config-router)#
*Jun 22 13:16:19.087: EIGRP-IPv4(100): table(default): route installed for
10.1.102.0/29 (90/21024000) origin(10.1.103.1)
10.1.102.0/29 (90/41024000) origin(10.1.203.2)
10.1.1.8/30 (90/20640000) origin(10.1.103.1)
*Jun 22 13:16:19.091: EIGRP-IPv4(100): table(default): 10.1.1.8/30 routing table
not updated thru 10.1.203.2
*Jun 22 13:16:19.091: EIGRP-IPv4
R3(config-router)#(100): table(default): route installed for 10.1.2.8/30
(90/21152000) origin(10.1.103.1)
10.1.2.8/30 (90/40640000) origin(10.1.203.2)
10.1.2.0/30 (90/21152000) origin(10.1.103.1)
10.1.2.0/30 (90/40640000) origin(10.1.203.2)
*Jun 22 13:16:19.091: EIGRP-IPv4(100): table(default): 10.1
R3(config-router)#.103.0/29 routing table not updated thru 10.1.203.2
10.1.1.4/30 (90/20640000) origin(10.1.103.1)
10.1.2.4/30 (90/21152000) origin(10.1.103.1)
10.1.2.4/30 (90/40640000) origi
R3(config-router)#n(10.1.203.2)
10.1.1.0/30 (90/20640000) origin(10.1.103.1)
*Jun 22 13:16:19.103: EIGRP-IPv4(100): table(default): 10.1.102.0/29 - do advertise
out Serial0/0/0
<output omitted>
g. Issue the show ip route command again to verify that there are now two routes to network 10.1.2.0. Notice that
the two routes have different (unequal) metrics (feasible distances).
R3# show ip route eigrp
D 10.1.1.0/30 [90/20640000] via 10.1.103.1, 00:05:56, Serial0/0/0
D 10.1.1.4/30 [90/20640000] via 10.1.103.1, 00:05:56, Serial0/0/0
D 10.1.1.8/30 [90/20640000] via 10.1.103.1, 00:05:56, Serial0/0/0
D 10.1.2.0/30 [90/40640000] via 10.1.203.2, 00:05:56, Serial0/0/1
[90/21152000] via 10.1.103.1, 00:05:56, Serial0/0/0
D 10.1.2.4/30 [90/40640000] via 10.1.203.2, 00:05:56, Serial0/0/1

[90/21152000] via 10.1.103.1, 00:05:56, Serial0/0/0
D 10.1.2.8/30 [90/40640000] via 10.1.203.2, 00:05:56, Serial0/0/1
[90/21152000] via 10.1.103.1, 00:05:56, Serial0/0/0
D 10.1.102.0/29 [90/41024000] via 10.1.203.2, 00:05:56, Serial0/0/1
[90/21024000] via 10.1.103.1, 00:05:56, Serial0/0/0
R3#
h. These unequal-cost routes also show up in the EIGRP topology table as an additional successor. Use the show
ip eigrp topology command to verify this. Notice there are two successor routes with different (unequal) feasible
distances.
via 10.1.103.1 (21024000/20512000), Serial0/0/0
via 10.1.203.2 (41024000/20512000), Serial0/0/1
via 10.1.103.1 (20640000/128256), Serial0/0/0
via 10.1.203.2 (40640000/128256), Serial0/0/1
via 10.1.103.1 (21152000/20640000), Serial0/0/0
via 10.1.203.2 (40640000/128256), Serial0/0/1
via 10.1.103.1 (21152000/20640000), Serial0/0/0
via 10.1.103.1 (20640000/128256), Serial0/0/0
via 10.1.203.2 (40640000/128256), Serial0/0/1
via 10.1.103.1 (21152000/20640000), Serial0/0/0
via 10.1.103.1 (20640000/128256), Serial0/0/0
R3#
i. Load balancing over serial links occurs in blocks of packets, the number of which are recorded in the routing
table’s detailed routing information. Use the show ip route 10.1.2.0 command to get a detailed view of how traffic
is shared between the two links. The traffic share counters represent the ratio of traffic over the shared paths. In
this case the ratio is 48:25 or about 2-to-1. The path through R1, 10.1.103.1, will be sent twice as much traffic as
the path through R2, 10.1.203.2. A traffic share count of 1 on all routes indicates equal cost load balancing. If the
traffic share count is 0, the path is not in use.
R3# show ip route 10.1.2.0
Routing entry for 10.1.2.0/30

Known via "eigrp 100", distance 90, metric 21152000, type internal
Redistributing via eigrp 100
Last update from 10.1.203.2 on Serial0/0/1, 00:10:11 ago
10.1.203.2, from 10.1.203.2, 00:10:11 ago, via Serial0/0/1
Route metric is 40640000, traffic share count is 25
Total delay is 25000 microseconds, minimum bandwidth is 64 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 3/255, Hops 1
* 10.1.103.1, from 10.1.103.1, 00:10:11 ago, via Serial0/0/0
Route metric is 21152000, traffic share count is 48
Total delay is 45000 microseconds, minimum bandwidth is 128 Kbit
Reliability 255/255, minimum MTU 1500 bytes
Loading 1/255, Hops 2
R3#
j. Check the actual load balancing using the debug ip packet command. Ping from R3 to 10.1.2.1 with a high
enough repeat count to view the load balancing over both paths. In the case above, the traffic share is 25 packets
routed to R2 to every 48 packets routed to R1.
To filter the debug output to make it more useful, use the following extended access list.
R3(config)# access-list 100 permit icmp any any echo
R3(config)# end
R3# debug ip packet 100
IP packet debugging is on for access list 100
R3# ping 10.1.2.1 repeat 50
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
*Jun 22 13:48:23.598: IP: s=10.1.103.3 (local), d=10.1.2.1 (Serial0/0/0), len 100,
sending
sending full packet
sending
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
sending full packet
sending
sending full packet
!
R3 just switched to load-share the outbound ICMP packets to Serial0/0/1.
!
sending

sending full packet
sending
*Jun 22 13:48:24.982: IP: s=10.1.203.3 (local), d=10.1.2.1 (Serial0/0/1
R3#), len 100, sending full packet
R3#
<output omitted>
Note: If a deliberate metric manipulation is necessary on a router to force it to prefer one interface over another for
EIGRP-discovered routes, it is recommended to use the interface-level command "delay" for these purposes. While
the "bandwidth" command can also be used to influence the metrics of EIGRP-discovered routes through a particular
interface, it is discouraged because the "bandwidth" will also influence the amount of bandwidth reserved for EIGRP
packets and other IOS subsystems as well. The "delay" parameter specifies the value of the interface delay that is
used exclusively by EIGRP to perform metric calculations and does not influence any other area of IOS operation.
k. Issue the show ip protocols command will verify the variance parameter and the number of maximum paths
used by EIGRP. By default, EIGRP will use a maximum of 4 paths for load balancing. This value can be changed
using the maximum-path EIGRP configuration command.
R3# show ip protocols
*** IP Routing is NSF aware ***
Routing Protocol is "application"
Sending updates every 0 seconds
Invalid after 0 seconds, hold down 0, flushed after 0
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Maximum path: 32
Routing for Networks:
Routing Information Sources:
Gateway Distance Last Update
Distance: (default is 4)
Routing Protocol is "eigrp 100"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates
Default networks accepted from incoming updates
EIGRP-IPv4 Protocol for AS(100)
Metric weight K1=1, K2=0, K3=1, K4=0, K5=0
NSF-aware route hold timer is 240
Router-ID: 10.1.3.9
Topology : 0 (base)
Active Timer: 3 min
Distance: internal 90 external 170
Maximum path: 4
Maximum hopcount 100
Maximum metric variance 2
Automatic Summarization: disabled
Maximum path: 4
Routing for Networks:
10.0.0.0
Routing Information Sources:
Gateway Distance Last Update

10.1.103.1 90 00:39:03
10.1.203.2 90 00:39:03
Distance: internal 90 external 170
R3#

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